(num_sign_bit_copies): At end, return 1 if NONZERO has the high bit set.

From-SVN: r4627

gcc/combine.c

@@ -6801,7 +6801,7 @@ num_sign_bit_copies (x, mode)
     return 1;
 
   nonzero = nonzero_bits (x, mode);
-  return (nonzero == GET_MODE_MASK (mode)
+  return (nonzero & ((HOST_WIDE_INT) 1 << (bitwidth - 1))
 	  ? 1 : bitwidth - floor_log2 (nonzero) - 1);
 }